Sea sparkle, which resembles fairy floss, gets its name because it may appear to be phosphorescent at night. A spokesman for the Metropolitan Sydney South Coast and Hunter Regional Algal Co-ordinating Committees, James Muddle, said the bloom was caused by a ''nutrient rich deep ocean water onto the continental shelf''.

He said sea sparkle had no known toxic effects other than it can cause a high level of ammonia when it starts to disintegrate so it can cause skin and eye irritation.

Algal experts said Noctiluca scintillans had probably caused the bloom seen on other Sydney and central coast beaches, including Clovelly, which was closed.